1. Field of the Invention
This invention relates to inert rigid vertebral prosthetic devices and methods for implanting the devices between adjacent vertebrae to treat or prevent back or neck pain in patients with ruptured or degenerated intervertebral discs and for replacing vertebral bodies damaged by fracture, tumor or degenerative process. Specifically, the invention deals with ring-like prosthetic plugs or discs used singly or stacked together between vertebrae to form support sturts in the spinal column and having rigid surfaces facilitating anchoring and providing valleys for bone ingrowth from adjoining vertebrae. The rings are bottomed on the opposing end faces of adjoining vertebrae, are preferably oval shaped with medial-lateral and anterior-posterior dimensions in the same ratio as normal vertebral bodies, are supplied in different heights to be used individually to replace a single damaged intervertebral disc, have ridges to bite into the vertebrae or to interdigitate to be securely stacked together to the exact height required at the time of surgery, have slots and hollow areas for packing bone graft material, tool receiving means, and are preferably radiolucent to allow visualization of the bone healing postoperatively.
2. Description of the Prior Art
While many types of vertebral prosthetic devices have been proposed, the success ratio has been very low and the surgical procedures have been very complicated and traumatic to the patient. The surgical implant devices and methods covered in my U.S. Pat. Nos. 4,743,256; 4,834,757 and 4,878,915 have greatly improved the success rate and have simplified the surgical techniques in interbody vertebral fusion. In the procedures covered by these patents, biologically acceptable but completely inert strut plugs are bottomed in channels or grooves of adjoining vertebrae and receive bone ingrowth which quickly fuses the structure to the bone and forms a living bone bridge across the fusion area.
The present invention now further improves this art of interbody fusion without cutting grooves or channels in the vertebrae and is especially well suited for anterior cervical and lumbar fusion. The invention provides ring-like prosthesis plugs or discs bottomed on end faces of adjoining vertebrae and constructed and arranged so that they can be used singly or stacked plurally to accommodate individual surgical requirements. The rings can replace excised discs and vertebrae and can also be mounted inside the fibrous disc column connecting adjoining vertebrae. The annular units are preferably oval or partial oval shaped preferably hemi-oval, to conform with vertebral disc shapes, have ridged or peaked surfaces for biting into the vertebrae on which they are seated and for receiving bone ingrowth in valleys between the peaks. When stacked, an interior connecting bar can be provided to lock the components in fixed relation and cooperate with interfitting ridges.